The present invention relates to electrical control systems for environmental conditioning equipment such as heat pumps.
Typically, environmental conditioning equipment, such as a heat pump, includes an electrical control system for monitoring selected variable conditions of the conditioned environment and of the conditioning equipment and for controlling various selected functions of the equipment in response to the monitored variables. Conventionally, the electrical control system comprises a thermostat connected by electrical wiring and temperature sensors, switches, and electrical relays. The relays control operation of selected components of the equipment. Electrical power is supplied directly to the thermostat which routes power to particular relays depending on the setting of the thermostat.
In modern equipment, the electrical control system may include an electronic control module including a microcomputer or other such device for receiving a plurality of electrical input signals, corresponding to various monitored variables, and for generating electrical outut signals, in response to the input signals, for controlling various functions of the environmental conditioning equipment according to preprogrammed procedures. The electrical input signals to the microcomputer may represent variables such as air temperature of the conditioned environment, temperatures at selected locations in the conditioning equipment, and positions of various switches. Through activation of appropriate electrical relays the microcomputer controls functions of the conditioning equipment by actuating valves and operating fans and motors. Efficiency is improved and operating capabilities of the equipment are increased by using such an electronic control module as part of the electrical control system for the equipment.
Normally, if an electronic control module fails then the electrical control system is disabled and it is not possible to operate the environmental conditioning equipment. Also, it is not possible to remove the control module for servicing and/or testing without shutting down the equipment. However, it is desirable to operate such equipment during time periods when the control module is being serviced, repaired, or tested.